There is a trend in the United States in recent years in mandating that a tire air pressure monitoring system be mounted in automobiles. Conventionally, there are systems that do not require a battery because of the use of a surface acoustic wave (SAW) device as a method for directly measuring the air pressure of a tire.
An RFID (Radio Frequency Identification) technique is known in which a wireless connection is provided between a tire-mounted pressure sensor and a controller on the vehicle body, and the two are electromagnetically coupled together. In a configuration that uses this RFID technique, an RFID transponder (RF tag) containing an inflation pressure sensor is disposed in the internal space of the tire, and a reader/writer is disposed on the vehicle body.